You don't necessarily have to cull them. I agree with getting one tested so you know what you are dealing with as some of these diseases are much worse to deal with and manage then others. I had an outbreak of infectious bronchitis three years ago. It went through all my birds but I only had 8 at the time. Took the first sick bird to my avian vet, he did a variety of tests and it came back as IB. We treated them all with antibiotic's as they became symptomatic since my rooster had quickly morphed right into pneumonia from all the junk in his respiratory system. Anyway, long story short, they all survived and have been fine every since.
